Listeria monocytogenes has received increasing attention as a human pathogen. Several documented outbreaks of listeriosis have been reported that have identified Listeria-contaminated food as the source of infection. In 1981 there was a major outbreak associated with cabbage, in 1983 with milk, and in 1985 there were more than 100 cases attributed to contaminated cheese.
The FDA has indicated that there is zero tolerance for Listeria in food. There have been several recent FDA recalls of products containing Listeria, generally consisting of dairy products, notably cheese and ice cream, some of which were imported. There have also been numerous company-initiated food product recalls.
Although there clearly exists a need for a reliable method to identify Listeria-contaminated food products, there is currently no easy or universally accepted method of culturing or confirming Listeria. The Association of Official Analytical Chemists (AOAC), the organization which validates methods of analysis for the food industry, has yet to approve any method to culture Listeria from food products. The FDA-suggested method requires lengthy cold enrichment culturing prior to testing. Other methods require elaborate instrumentation for data analysis.
Listeria is a gram-positive, non-sporeforming, motile rod, which has the capacity to grow over a wide range of temperatures (4.degree. C. to 45.degree. C.). It has been reported to be antigenically related to other gram positive organisms such as Staphylococcus aureus and Streptococcus fecalis. Consequently, an immunodiagnostic approach to Listeria identification requires very specific antibodies. We have produced and characterized a series of murine monoclonal antibodies that identify a genus-specific Listeria antigen, with which we have been successful in developing a diagnostic assay.